Automobile suspension system

Abstract

An automobile suspension system comprises a front suspension having at least a spring placed between sprung and unsprung masses to support the sprung mass thereon and a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound, and a rear suspension having at least a spring placed between the sprung and unsprung masses to support the sprung mass thereon and a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound. Vertical downward jacking-force characteristics of the front suspension is set to be stronger relatively with respect to vertical downward jacking-force characteristics of the rear suspension during cornering.

What is claimed is: 
     
       1. An automobile independent suspension system comprising: a front independent suspension having at least a spring placed between sprung and unsprung masses to support the sprung mass thereon, and a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound; and   a rear independent suspension having at least a spring placed between the sprung and unsprung masses to support the sprung mass thereon, and a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound;   wherein vertical downward jacking-force characteristics of said front suspension is set to be stronger relatively with respect to vertical downward jacking-force characteristics of said rear independent suspension, so that a front end of the vehicle is operated in a falling mode relatively with respect to a rear end of the vehicle during cornering.   
     
     
       2. An automotive front independent suspension system comprising: a spring placed between sprung and unsprung masses to support the sprung mass thereon; and   a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound,   wherein said front independent suspension system has a spring constant k fA  at each of front-left and front-right road wheels of an automotive vehicle on extension during rebound and a spring constant k fB  at each of the front-left and front-right road wheels of the vehicle on compression during bound,   wherein a ratio ε f  (=k fB  /k fA ) of said spring constant k fB  on compression during bound to said spring constant k fA  on extension during rebound is determined to satisfy the following inequality, so that a vertical downward jacking-force component is created at a front end of the vehicle and the front end of the vehicle is operated in a falling mode relatively with respect to a rear end of the vehicle during cornering, ##EQU17## where φ is a roll angle of the vehicle and is equal to Wαh/(K f  +K r ), W is a car weight, α is a centripetal acceleration exerted on the vehicle, K f  is a roll stiffness of a front wheel side, K r  is a roll stiffness of a rear wheel side, h is a height of center of gravity of the vehicle, h f0  is an initial height of roll center of the front wheel side, t is a track being equivalent to a traverse distance between left and right road wheels on a front axle, and a f  is a rate of change in the roll center of the front wheel side with respect to a front-suspension stroke.   
     
     
       3. An automobile front independent suspension system comprising: a spring placed between sprung and unsprung masses to support the sprung mass thereon; and   a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound,   wherein the shock absorber of said front independent suspension system has a first auxiliary spring placed at each of front-left and front-right ends of an automotive vehicle for suppressing rebound and a second auxiliary spring placed at each of the front-left and front-right ends of the vehicle for suppressing bound,   wherein a spring constant of said first auxiliary spring is set to be greater than a spring constant of said second auxiliary spring, so that a vertical downward jacking-force component is created at a front end of the vehicle and the front end of the vehicle is operated in a falling mode relatively with respect to a rear end of the vehicle during cornering.   
     
     
       4. An automobile rear independent suspension system comprising: a spring placed between sprung and unsprung masses to support the sprung mass thereon; and   a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound,   wherein said rear independent suspension system has a spring constant k rA  at each of rear-left and rear-right road wheels of an automotive vehicle on extension during rebound and a spring constant k rB  at each of the rear-left and rear-right road wheels of the vehicle on compression during bound,   wherein a ratio ε r  (=k rB  /k rA ) of said spring constant k rB  on compression during bound to said spring constant k rA  on extension during rebound is determined to satisfy the following inequality, so that a vertical upward jacking-force component is created at a rear end of the vehicle and the rear end of the vehicle is operated in a rising mode relatively with respect to a front end of the vehicle during cornering, ##EQU18## where φ is a roll angle of the vehicle and is equal to Wαh/(K f  +K r ), W is a car weight, α is a centripetal acceleration exerted on the vehicle, K f  is a roll stiffness of a front wheel side, K r  is a roll stiffness of a rear wheel side, h is a height of center of gravity of the vehicle, h r0  is an initial height of roll center of the front wheel side, t is a track being equivalent to a traverse distance between left and right road wheels on a rear axle, and a r  is a rate of change in the roll center of the rear wheel side with respect to a rear-suspension stroke.   
     
     
       5. An automobile rear independent suspension system comprising: a spring placed between sprung and unsprung masses to support the sprung mass thereon; and   a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound,   wherein the shock absorber of said rear independent suspension system has a first auxiliary spring placed at each of rear-left and rear-right ends of an automotive vehicle for suppressing rebound and a second auxiliary spring placed at each of the rear-left and rear-right ends of the vehicle for suppressing bound,   wherein a spring constant of said second auxiliary spring is set to be greater than a spring constant of said first auxiliary spring, so that a vertical upward jacking-force component is created at a rear end of the vehicle and the rear end of the vehicle is operated in a rising mode relatively with respect to a front end of the vehicle during cornering.   
     
     
       6. An automobile independent suspension system comprising: a front independent suspension having at least a spring placed between sprung and unsprung masses to support the sprung mass thereon, and a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound; and   a rear independent suspension having at least a spring placed between the sprung and unsprung masses to support the sprung mass thereon, and a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound,   wherein said front independent suspension has a spring constant k fA  at each of front-left and front-right road wheels of an automotive vehicle on extension during rebound and a spring constant k fB  at each of the front-left and front-right road wheels of the vehicle on compression during bound,   wherein said rear independent suspension has a spring constant k rA  at each of rear-left and rear-right road wheels of the vehicle on extension during rebound and a spring constant k rB  at each of the rear-left and rear-right road wheels of the vehicle on compression during bound,   wherein said spring constant k fA , k fB , k rA  and k rB  are determined to satisfy the following inequality, so that a rear end of the vehicle is operated in a rising mode relatively with respect to a front end of the vehicle during cornering, ##EQU19## where φ is a roll angle of the vehicle and is equal to Wαh/(K f  +K r ), W is a car weight, α is a centripetal acceleration exerted on the vehicle, K f  is a roll stiffness of a front wheel side, K r  is a roll stiffness of a rear wheel side, h is a height of center of gravity of the vehicle, γ is a car-weight distribution rate of the front road wheels with respect to the rear road wheels, h f0  is an initial height of roll center of the front wheel side, h r0  is an initial height of roll center of the rear wheel side, t is a track being equivalent to a traverse distance between left and right road wheels, a f  is a rate of change in the roll center of the front wheel side with respect to a front-suspension stroke, and a r  is a rate of change in the roll center of the rear wheel side with respect to a rear-suspension stroke.   
     
     
       7. A method of controlling lacking characteristics at an automobile front independent suspension system having at least a spring placed between sprung and unsprung masses to support the sprung mass thereon, and a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound, the method comprising: determining a lateral load transfer ΔW f  of a front independent suspension during a steady-state cornering, using the following expression,   ΔW.sub.f =Wγαh/t        where W is a car weight, γ is a car-weight distribution rate of front road wheels with respect to rear road wheels, α is a centripetal acceleration exerted on an automotive vehicle, h is a height of center of gravity of the vehicle, and t is a track being equivalent to a traverse distance between left and right wheels on a front axle;   determining a cornering force F fA  of a front inner wheel and a cornering force F fB  of a front outer wheel, using the following expression,   F.sub.fA Wαγ(1/2-αh/t)       F.sub.fB Wαγ(1/2+αh/t);        determining an angle θ fA  between a horizontal line and a line segment including a center of a front inside tire contact and a front inside wheel roll-center height, and an angle θ fB  between the horizontal line and a line segment including a center of a front outside tire contact and a front outside wheel roll-center height, using the following expression,   θ.sub.fA =a.sub.f φ+2h.sub.f0 /t-φ       θ.sub.fB =-a.sub.f φ+2h.sub.f0 /t+φ        where φ is a roll angle of the vehicle and is equal to Wαh/(K f  +K r ), K f  is a roll stiffness of a front wheel side, K r  is a roll stiffness of a rear wheel side, h f0  is an initial height of roll center of the front wheel side, and a r  is a rate of change in the roll center of the front wheel side with respect to a front-suspension stroke;   determining a vertical downward jacking force J fA  created at the front inside wheel and a vertical upward jacking force J fB  created at the front-outside wheel, using the following expression, ##EQU20## determining, during the steady-state cornering, a steady-state rebound amount Z fA  of the front inside wheel and a steady-state bound amount Z fB  of the front outside wheel, using the following expression,   Z.sub.fA =(ΔW.sub.f -J.sub.fA)/k.sub.fA       Z.sub.fB =(ΔW.sub.f -J.sub.fB)/k.sub.fB        where k fA  is a spring stiffness at each front end of the vehicle on extension during rebound and k fB  is a spring stiffness at each front end of the vehicle on compression during bound;   determining a ratio ε f  (=k fB  /k fA ) of said spring stiffness k fB  on compression during bound to said spring stiffness k fA  on extension during rebound, using the following expression which satisfies a condition defined by an inequality Z fA  ≦Z fB  according to which a front end of the vehicle is operated in a falling mode being equivalent to stronger vertical downward jacking-force characteristics during cornering, ##EQU21##  controlling jacking characteristics of said front independent suspension based on a suspension stiffness characteristics having said spring stiffness k fB  on compression during bound and said spring stiffness k fA  on extension during rebound, said ratio ε f  (=k fB  /k fA ) of said spring stiffness k fB  to said spring stiffness k fA  being determined to satisfy said expression.   
     
     
       8. A method of controlling jacking characteristics at an automobile rear independent suspension system having at least a spring placed between sprung and unsprung masses to support the sprung mass thereon, and a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound, the method comprising: determining a lateral load transfer ΔW r  of a rear independent suspension during a steady-state cornering, using the following expression,   ΔW.sub.r =W(1-γ)αh/t        where W is a car weight, γ is a car-weight distribution rate of front road wheels with respect to rear road wheels, α is a centripetal acceleration exerted on an automotive vehicle, h is a height of center of gravity of the vehicle, and t is a track being equivalent to a traverse distance between left and right wheels on a rear axle;   determining a cornering force F fA  of a front inner wheel and a cornering force F fB  of a front outer wheel, using the following expression,   F.sub.fA =αW(1-γ)·{1/2-αh/t}       F.sub.fB =αW(1-γ)·{1/2+αh/t};        determining an angle θ rA  between a horizontal line and a line segment including a center of a rear inside tire contact and a rear inside wheel roll-center height, and an angle θ rB  between the horizontal line and a line segment including a center of a rear outside tire contact and a rear outside wheel roll-center height, using the following expression,   θ.sub.rA =a.sub.r φ+2h.sub.r0 /t-φ       θ.sub.rB =a.sub.r φ+2h.sub.r0 /t+φ        where φ is a roll angle of the vehicle and is equal to wαh/(K f  +K r ), K f  is a roll stiffness of a front wheel side, K r  is a roll stiffness of a rear wheel side, h r0  is an initial height of roll center of the rear wheel side, and a r  is a rate of change in the roll center of the rear wheel side with respect to a rear-suspension stroke;   determining a vertical downward jacking force J rA  created at the rear inside wheel and a vertical upward jacking force J rB  created at the rear-outside wheel, using the following expression, ##EQU22##  determining, during the steady-state cornering, a steady-state rebound amount Z rA  of the rear inside wheel and a steady-state bound amount Z rB  of the rear outside wheel, using the following expression,   Z.sub.rA =(ΔW.sub.r -J.sub.rA)/k.sub.rA       Z.sub.rB =(ΔW.sub.r -J.sub.rB)/k.sub.rB     where k rA  is a spring stiffness at each rear end of the vehicle on extension during rebound and k rB  is a spring stiffness at each rear end of the vehicle on compression during bound;     determining a ratio ε r  (=k rB  /k rA ) of said spring stiffness k rB  on compression during bound to said spring stiffness k rA  on extension during rebound, using the following expression which satisfies a condition defined by an inequality Z rA  ≦Z rB  according to which a rear end of the vehicle is operated in a rising mode being equivalent to stronger jack-up characteristics during cornering, ##EQU23##  controlling jack-up characteristics of said rear independent suspension based on a suspension stiffness characteristics having said spring stiffness k rB  on compression during bound and said spring stiffness k rA  on extension during rebound, said ratio ε r  (=k rB  /k rA ) of said spring stiffness k rB  to said spring stiffness k rA  being determined to satisfy said expression.   
     
     
       9. A method of controlling jacking characteristics at an automobile independent suspension system employing a front independent suspension having at least a spring placed between sprung and unsprung masses to support the sprung mass thereon and a shock absorber placed between the sprung and unsprung masses to regulate spring rebound and bound and a rear independent suspension system having at least a spring placed between the sprung and unsprung masses to support the sprung mass thereon and a shock absorber placed between the sprung and unsprung mosses to regulate spring rebound and bound, the method comprising: determining lateral load transfers ΔW f  and ΔW r  of the front and rear independent suspensions during a steady-state cornering, using the following expression,   ΔW.sub.f =Wγαh/t       ΔW.sub.r =W(1-γ)αh/t        where W is a car weight, γ is a car-weight distribution rate of front road wheels with respect to rear road wheels, α is a centripetal acceleration exerted on an automotive vehicle, h is a height of center of gravity of the vehicle, and t is a track being equivalent to a traverse distance between left and right wheels;   determining a cornering force F fA  of a front inner wheel, a cornering force F fB  of a front outer wheel, a cornering force F rA  of a rear inner wheel, and a cornering force F rB  of a rear outer wheel, using the following expression,   F.sub.rA =Wαγ(1/2-αh/t)       F.sub.fB =Wαγ(1/2-αh/t)       F.sub.rA =αW(1-γ)·{1/2-αh/t}       F.sub.rB =αW(1-γ)·{1/2+αh/t}        determining an angle θ fA  between a horizontal line and a line segment including a center of a front inside tire contact and a front inside wheel roll-center height, an angle θ fB  between the horizontal line and a line segment including a center of a front outside tire contact and a front outside wheel roll-center height, an angle θ rA  between the horizontal line and a line segment including a center of a rear inside tire contact and a rear inside wheel roll-center height and an angle θ rB  between the horizontal line and a line segment including a center of a rear outside tire contact and a rear outside wheel roll-center height, using the following expression,   θ.sub.fA =a.sub.f φ+2h.sub.f0 /t-φ       θ.sub.fB --a.sub.r φ+2h.sub.f0 /t+φ       θ.sub.rA =a.sub.r φ+2h.sub.r0 /t-φ       θ.sub.rB =-a.sub.r φ+2h.sub.r0 /t+φ        where φ is a roll angle of the vehicle and is equal to Wαh/(K f  +K r , K f  is a roll stiffness of a front wheel side, K r  is a roll stiffness of a rear wheel side, h f0  is an initial height of roll center of the front wheel side, and a f  is a rate of change in the roll center of the front wheel side with respect to a front-suspension stroke, h r φ  is an initial height of roll center of the rear wheel side, a r  is a rate of change in the roll center of the rear wheel side with respect to a rear-suspension stroke;   determining a vertical downward jacking force J fA  created at the front inside wheel, a vertical upward jacking force J fB  created at the front-outside wheel, a vertical downward jacking force J rA  created at the rear inside wheel, and a vertical upward jacking force J rB  created at the rear-outside wheel, using the following expression, ##EQU24##  determining, during the steady-state cornering, a steady-state rebound amount Z fA  of the front inside wheel, a steady-state bound amount Z fB  of the front outside wheel, a steady-state rebound amount Z rA  of the rear inside wheel, and a steady-state bound amount Z rB  of the rear outside wheel, using the following expression,   Z.sub.fA =(ΔW.sub.f -J.sub.fA)/k.sub.fA       Z.sub.fB =(ΔW.sub.f -J.sub.fB)/k.sub.fB       Z.sub.rA =(ΔW.sub.r -J.sub.rA)/k.sub.rA       Z.sub.rB =(ΔW.sub.r -J.sub.rB)/k.sub.rB     where k fA  is a spring stiffness at each front end of the vehicle on extension during rebound, k rB  is a spring stiffness at each front end of the vehicle on compression during bound, k rA  is a spring stiffness at each rear end of the vehicle on extension during rebound, and k rB  is a spring stiffness at each rear end of the vehicle on compression during bound;   determining said spring stiffnesses k fA , k fB , k rA  and k rB , using the following expression which satisfies a condition defined by an inequality Z fB  -Z fA  ≦-Z rB  -Z rA  according to which a front end of the vehicle is operated in a falling mode being equivalent to stronger vertical downward jacking-force characteristics, relatively with respect to the rear end of the vehicle during cornering, ##EQU25##  controlling jacking characteristics of said front independent suspension based on a suspension stiffness characteristics having said spring stiffness k fB  on compression during bound and said spring stiffness k fA  on extension during rebound, and on a suspension stiffness characteristics having said spring stiffness k rB  on compression during bound and said spring stiffness k rA  on extension during rebound, said spring stiffnesses k fA , k fB , k rA  and k rB  being determined to satisfy said expression.